Irvine, Calif. — Freshwater runoff from the Sierra Nevada may decrease by as much as one-quarter by 2100 due to climate warming on the high slopes, according to scientists at UC Irvine and UC Merced.

Accelerated plant growth at higher elevations caused by increasing temperatures would trigger more water absorption and evaporation, accounting for the projected runoff declines, the researchers add.

A diminished river flow will only add to the burden of providing resources to the thirsty farms and homes that rely on it. The state is currently experiencing a severe drought, and some reservoirs and groundwater levels are at all-time lows.

The study findings appear this week in the early online edition of Proceedings of the National Academy of Sciences.

“Scientists have recognized for a while that something like this was possible, but no one had been able to quantify whether it could be a big effect,” said UCI professor of Earth system science Michael L. Goulden of the decreased runoff. “It’s clear that this could be a big effect of climate warming and that water managers need to recognize and plan for the possibility of increased water losses from forest evaporation.”

According to the researchers, runoff from mountain ranges is vulnerable to temperature hikes that lengthen growing seasons and result in more vegetation growth at high elevations. Snow-dominated mountain forests that are currently dormant in winter with cold temperatures have lower vegetative density and less evapotranspiration than downslope forests in the snow-rain transition zone, which have year-round growing seasons. Evapotranspiration is the combination of water evaporation from land and the loss of water through plant-leaf transpiration.

Goulden and UC Merced’s Roger C. Bales investigated the potential influence of a warming climate on evapotranspiration in the Kings River Basin in California’s Sierra Nevada and found resulting changes in the amount of freshwater mountain runoff available to serve surrounding communities.

They gauged water vapor emission rates and combined those measurements with remote sensing imagery to determine relationships among elevation, climate and evapotranspiration. According to the data, freshwater mountain runoff is highly sensitive to expanded vegetation growth.

The authors found that greater vegetation density at higher elevations in the Kings basin with the 4.1 degrees Celsius warming projected by climate models for 2100 could boost basin evapotranspiration by as much as 28 percent, with a corresponding 26 percent decrease in river flow.

Further, the relationships among evapotranspiration, temperature and vegetation density were similar across a broader area of the Sierra Nevada, suggesting that the impact of climate change on evapotranspiration and freshwater availability could be widespread.

“Most people have heard about the giant forests around Yosemite and Sequoia national parks, but these areas have not been a focus of this type of research. Understanding of Sierran hydrology has improved recently with the National Science Foundation’s Critical Zone Observatory, and data collected there allowed us to look at the problem from several perspectives,” Goulden said. “All of our analyses pointed in the same direction: An upslope expansion of forest with warming would cause a large increase in evaporative water loss and lead to reduced water availability.”

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Bales is a professor of engineering and director of the Sierra Nevada Research Institute at UC Merced. The research was supported by the NSF, through the Southern Sierra Critical Zone Observatory (EAR-0725097) and a major research instrumentation grant (EAR-0619947), and by the U.S. Department of Energy’s Terrestrial Ecosystem Science program.

what a load of hogwash. Water is too serious a matter to let fools like that play with failed computer models. Anyone who extrapolates out that far is not a scientist of any repute or regard. We have to use what water we have in much better ways and technology is rapidly advancing in this area.
That advance must not be blocked by these dopes trying to grab so me more climate funding.

The loss of ground water to trees is no model. One of the worst consequences of “only you can prevent forest fires” was the drastic increase in the numbers of trees per acre in most of the lower 48 since the end of the 19th C. I have heard from good authorities that there are more trees within the US borders now than there were 200 years ago. Fire suppression also encouraged development of dense undergrowth and understory formation which fire fighters of my acquaintance refer to as “fire ladders.” The reason given is that a small fire in the duff can burn merrily along until it encounters brush, climb into the brush, thence into understory trees and from there into the overstory crown. It was preventing forest fires that made them worse. One cause of lowered incidence of major fires in the west may be due to the hands-off, defensive approach now employed by many forests in fire suppression.

One of the consequences of dense tree stands is increased depth to ground water, and as the water elevation drops the trees compete with each other. A forester working with the Willamette N.F. in Oregon pointed out square miles of dead trees that had essentially “fought to the death” for declining water. Seriously thinning forests is a means of increasing surface water supply and I have seen it convert seasonal streams to perennial streams, and intermittent streams to seasonal streams on ranches in the Sierra Nevada foothills and in the Coast Ranges in California. Not everything about climate is temperature, and not everything about climate change is NOT anthropogenic. We do have an influence, just not usually what “the Team” talks about.

The problem is really one of unbounded funding.
Why governments have been suckered into approving this enormous waste of taxpayers money is beyond me
With so many real problems facing every country, this climate overstudy nonsense is both reprehensible and just plain STUPID!

Your “there is good science that says this [drought] may cause stress to the San Andreas Fault” is not supported by the article you linked. It says that extensive groundwater pumping “makes it a bit easier for the plates to slide, which might set off subtle shudders“. Sounds to me like groundwater loss eases the stress slightly.

Peter you should actually read the articles you link before you (incorrectly) comment on them.
It is not the draught per se, that causes tectonic strain, according to the article but rather the seasonal changes of alternate of snow and rain load followed by summertime relief from the precipitation load. According to their hypothesis a prolonged drought would reduce stress on the SA fault.

Droughts suck but have little to do with CO2. Building in a desert is the real problem… The irony is the panic of increased CO2 will run uncontrolled. But when alarmists acknowledge flora is a negative feedback, suddenly flora is the cause for alarm. I’m pretty sure not everything that happens in the world is panic worthy…

More trees will not mean more CO2 absorption? Really? Not to mention all the other non-tree foliage that will accompany the trees. You made your statement as if you already know the precise amount of vegetation that will result in a bit of warming. And what of the evaporation rate? More evaporation means more rain. More rain means more cloud coverage. More cloud coverage means a cooler surface.

Sounds more and more like there’s too many people in California – it is characteristically incapable of supporting so many people in the style and comfort they’ve raped the land to produce. Let the Owens river run free and relocate the hungry and parched climate refugees to New England, the other leftist coast.

The left coast really is the left coast. Geographically speaking the majority of Calif is conservative.
The water shortage is primarily political, despite the current and real drought. We flush a lot of water to the ocean for a little fish, the CA smelt. The greens have shut down any new reservoirs for decades.

Just a dry spell if you live here. As regards “flushing water” anywhere, a very large number of delta ranchers aren’t in favor of tunnels or, for that matter, pumping water to So. Cal., or even south into the desert called the southern San Joaquin Valley. If you know what you are looking for, evidence of the past failures of long distance water transport to make perfectly good grazing land useable as cropland are all over the Great Valley. Besides, smelt are decent eating when you can take them legally. You can’t say that about an inhabitant of L.A.

Stunning,.. the CAGW types only see DOOM and GLOOM in every thing they study. When it comes to CO2 fertilizing food crops, they focus on the 5% reduction on possible minerals and the fact that the bugs will find them more attractive to eat. It is to the point that I think these people need to be on meds.

In addition to all the positive benefits gained from a slightly warmer Earth this “researcher” mentioned, isn’t it funny he completely failed to mention the CO2 fertilization effect, which will further increase plant growth, crop yields and forest growth by 50% once CO2 levels hit 560ppm? (Idso & Idso et al).

How will nature and humans ever adapt to a greener and more fertile planet that’s better able to feed and support more life?

Oh, the humanity….

Moreover, increased ocean evaporation from slightly warmer global temps would more than offset any incremental loss of evaporation from tree lines moving to higher altitudes/latitudes…

I forgot to mention that the, “4.1 degrees Celsius warming projected by climate models for 2100”, cited in this paper is now a completely implausible scenario.

Such an absurd CAGW warming projection would require CO2 induced warming to be 0.38C/decade every year for the next 86 straight years, starting from tomorrow, to achieve such a huge amount of CO2 induced warming….

Too bad for the CAGW grant swindlers that there hasn’t been ANY global warming trend for the past 15~18 years (depending on temp database used), despite 1/3rd of all man-made CO2 emissions since 1750 (not a typo) made over just the last 18 years..

Not even the IPCC will admit 0.38C/decade of CO2 forcing is even remotely possible for the next 86 straight years…

I guess they never leave the air-conditioned office.
Trees, foothill forests prolong river flow throughout the year.
The forest acts as a sponge for snowmelt, downpours and so on, thus preventing flooding and then their real value kicks in, come midsummer the water flow is clean, cool and steady.
Known in many farming areas where the forests were cleared ruthlessly to create farm land.
Until the foothill forests grew back, there was spring flooding and summer drought.

‘“Scientists have recognized for a while that something like this was possible, but no one had been able to quantify whether it could be a big effect,” said UCI professor of Earth system science Michael L. Goulden of the decreased runoff. ‘

‘ recognized for a while’? When the dams don’t fill because of reduced runoff, because it is not PC to maintain good runoff drains, has been known for decades.

This shall not help the historic (dare I say “unprecedented”) anthropogenic aquifer depletion, some areas will already need a thousand years of steady rain to recharge, or more. Compare maps:
Used in Wikipedia “Sierra Nevada” entry:

Naturally clouds from the Pacific move inland to the Sierra Nevada range, which yields precipitation. But the area of greatest depletion is in this “rain shadow” of the mountain range, incoming is far less than outgoing. With less freshwater runoff, the situation will worsen.

Question for experts: With the aquifer depletion there is subsidence, which can happen suddenly. Does the area of great aquifer depletion indicate an area with a pattern of minor earthquakes?

The water shortages and riots will happen shortly without action. If California doesn’t build desalinization plants soon, as in build and not just start another multi-decade environmental review and blocking lawsuit cycle, smart people should evacuate. As if anyone needed another reason to get away from Krazy Kalifornia.

It’s absurd that California has not spent more on desalinization plants given its population growth and its semi-desert climate.

Many desalinization plants have been proposed, but the EPA and enviro-wacko advocacy groups have prevented their development.

Another problem in California is the cyclical nature of its precipitation, which closely follows El Nino/La Nina cycles. Stupid political hacks often propose building desalinization plants during dry La Nina cycles, and then defund the projects once El Nino/high precipitation cycles restart….

The US should follow Singapore’s model of rapid desalinization plant development to address their water shortage problem.

In the future, cheap and abundant waste heat from Liquid Fluoride Thorium Reactors will eventually supply arid areas of the country with more fresh water than they’ll know what to do with…

Until LFTRs are available, reverse osmosis desalinization plants must rapidly be built in California to meet its growing water requirements.

The only CO2 problem is the Earth has already sequestered away too much as carbonate, the plants would like much more to grow better.

With the desalinization water you can have greenhouses, the “carbon emissions” from the coal-fired energy stations can be pumped through the greenhouses where they will be happily received by the plants.

Don’t forget to first use the incoming seawater as cooling water for the coal-fired energy stations before sending it to desalinization pre-warmed. Perhaps it can be engineered as part of the desalinization, convert seawater to steam to drive the turbines, then condense the freshwater. Total commercial products from burning coal: potable water, sea salt, happy fresh produce, coal ash.

You should be happy to know coal ash has many uses, including as a partial replacement of Portland cement in concrete which greatly increases its durability. Thus by displacing the cement, the carbon footprint of the concrete is reduced.

That’s because idiot politicians didn’t know about Australia’s drought and deluge aquifer cycle, but they did know jumping on the CAGW bandwagon got them votes and political support including financial.

This in the US is different, we’ve pumped down aquifers until the ground is sinking in and seawater is infiltrating. See the link, around Chicago they’re down 900 feet, and that’s next to Lake Michigan. I wouldn’t be surprised to see Chicago swallowed up in a chasm from a subsurface channel of inflowing water that eroded the bedrock.

Looking for an updated report on the central valley water table. Most of the initial depletion happened prior to 1985, with some land subsiding up to 60′. By about 1985, for a time, water table decline flattened, and even rose in the northern areas of the central valley. This was partially due to extensive canals that actually acted as mini rivers, losing water into the ground water table. In the last ten years, despite some areas being denied water, many wineries were approved, and many fruit and some nut trees have been abandoned and torn out. It is a solvable problem, even in severe droughts like the current one, but not in todays political non-sense thought.

There is no CO2 problem other than those created by the current political stupidity.
Now get back to discussing REAL environmental problems, there are plenty, and maybe we can work together on real solutions.

I grew up arguing for paper and glass recycling when it all went into landfill. Now I’m sick of hearing all this so-called “ecological” crap. I’m not some redneck neoconservative republican but I’m sick of it.

Horoscope:
Aries – You are gonna die.
Cancer – You are gonna die.
Leo – You are gonna die.
Scorpio – You are gonna die.
Pisces – You are gonna die.
Taurus – You are gonna die.
Gemini – You are gonna die.
Virgo – You are gonna die.
Libra – You are gonna die.
Sagittarius – You are gonna die.
Capricorn – You are gonna die.
Aquarius – You are gonna die.

“The authors found that greater vegetation density at higher elevations in the Kings basin with the 4.1 degrees Celsius warming projected by climate models for 2100 could boost basin evapotranspiration by as much as 28 percent, with a corresponding 26 percent decrease in river flow.”

Given how accurately climate models have predicted projected warming hitherto, I would suggest moderated terror.

am i right that none of this is based on the results of analyzing actual data? they took the results of what a climate model predicts will happen to temps in 2100 and plugged them into another model that predicts runoff levels in the predicted climate of the year 2100…

No doubt contributing to Omega drought . Suspect they may be forgetting the CO2 fertilization. Imagine all those doggone plants up there sucking up our rightful water and sinful CO2 to put Oxygen in the atmosphere!

If you want more water shed from the highlands get rid of the trees and brush! Kill Smoky the Bear! The stories you have been fed are lies. The Indians and old timers knew this and created the conditions that maximized water and food production from these areas. Modern practices maximize fire storm fueled conditions of high fuel accumulations and die off from soil water depletion under that growth. Trees and brush suck springs dry and deplete the shallow water tables. They use as much water as a real irrigated farm field!. pg

Peter, Peter, Peter, this is models all the way down, and models ignorant of history to boot. From your paper”…and the risk of an unprecedented 50 year megadrought is non-negligible under the most severe warming scenario (5-10%…”
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Calif has had two 100 plus year droughts in the last 1000 years.

Interesting. David A points out two issues (over reliance on models and the ‘unprecedented’ scare word) and Peter responds with an appeal to authority. They are probably right though, 100 years is not the same as 50, so it is possible that if the drought went to 50 years, even though it has gone longer, it would be unprecedented unless you can show another went exactly 50 years. They got you there David.

A diminished river flow will only add to the burden of providing resources to the thirsty farms and homes that rely on it. The state is currently experiencing a severe drought, and some reservoirs and groundwater levels are at all-time lows.

Have any of these idiots actually been up to the high altitudes in the Sierras lately? I have been in the past few weeks and have pictures from friends who were up there this weekend and recent rains have completely replenished the lakes above 10,000 feet. Also, if you are up there, where is the most moisture, where there are no plants and trees? Nope, where there are trees, there is moisture, and it retains that moisture to run into the lakes during the dry summer months and precludes rapid evaporation that otherwise happens at the high altitudes.

I live in the Sierras and have also been in the high country. It has been a relatively wet August in the high country, but little of it has found its way down to lower reservoirs. Every little bit helps though.

“Trees are now evil.” Not really, trees became “evil” to these charlatans long ago the minute they started carping about “sustainability”. Bio-fuel, solar panels and wind turbines are already the enemies of the forest and everything that lives there. Coal and crude are what saved US forests from complete decimation in the 1800’s.

Models say 4 degrees, my guess 0.8 maximum given current hiatus projected to continue for 20 to 30 years. This is being generous. Therefore divide the result by say 5 gives 5% increase. If we knew the margin of error for this research given it is climate and widely variable. The real answer is probably with the margin of error 100 years out.

Increasing the temp a few degrees may increase the biomass accumulation rate. If so, it will sequester CO2. It will increase the water vapour content of the air and promote rainfall. If the density is great enough it will create a damp, wet microclimate that retains moisture well.

The claim about drought sounds very unlikely. Recreating forests slopes improves groundwater retention and runoff goes up because trees harvest water from fog at high elevations. Examples of this exist in Chile and the Giant Sequoia National Forest.

Trees shade the ground are reduce evaporation of rainfall. They also harvest snow as already noted above. They reduce sublimation of the snowpack. Trees are altogether good. Remove them and reduce surface water resources. This has been well known for over a century. Refer to books by Dr St. Barber Baker and Men of The Trees for additional information.

“Look, I barely passed science in high school so I don’t know much, but one thing I have learned is that climate scientists have an enormous regard to climate history. So much so that it occupies the bulk of their research.”

So much so that they are constantly rewriting it make sure it fits thier model output.

Abstract – 24 Nov 2011Potential increase in floods in California’s Sierra Nevada under future climate projections
…….By the end of the 21st Century, all projections yield larger-than-historical floods, for both the Northern Sierra Nevada (NSN) and for the Southern Sierra Nevada (SSN). The increases in flood magnitude are statistically significant (at p <= 0.01) for all the three GCMs in the period 2051–2099. The frequency of flood events above selected historical thresholds also increases under projections from CNRM CM3 and NCAR PCM1 climate models, while under the third scenario, GFDL CM2.1, frequencies remain constant or decline slightly, owing to an overall drying trend. These increases appear to derive jointly from increases in heavy precipitation amount, storm frequencies, and days with more precipitation falling as rain and less as snow. Increases in antecedent winter soil moisture also play a role in some areas…….http://link.springer.com/article/10.1007/s10584-011-0298-z

One solution is to bulldoze the activists out of the way and build more water reservoirs. Incidentally, the rain over the Ogalla reservoir, even in TX, OK, NB etc. has been much more copious this year. Natural recharge can take a long time but perhaps we should take a leaf out of the oil and gas notebook and artificially recharge the aquifers when rain does come. Capture a lot more of it in reservoirs and the demand from aquifers is also greatly reduced. I guess we are stuck with the expense of empty-headed activists misanthropists against everything. Ironically, they can only thrive in an economy that creates the prosperity and abundance of dollars to keep them unproductive. Not a lot of this activism in 150 countries or so. If you want to know the end game of a long term successful social activist campaign against capitalism and the innovation and prosperity it creates, look at the winner of the earth day lights-out contest every year – North Korea. They have the lowest carbon and every other form of footprint in the world.

Peter asks if any of us dispute this article…. Hell no! More trees are another benefit of CO2, and I could list dozens. There are no concerns with increased levels since the next 10,000 ppm’s could not match the very first 100 ppm’s in warming effect.
More trees mean less uncontrolled runoff. The water still reaches the lakes, or sinks into the aquifers, and less floods out into the Pacific. The additional trees will hold the snow longer and release it slower.
There is no current downside to increased CO2, and only computer climate video games believe in the science fiction of dangerous warming.

Any possibility that the increased evapotranspiration will result in greater rainfall further down wind? Seems to me I’ve read that increased forest cover often leads to increased rainfall. Maybe not here, but has the question been studied?

Ah, I see their problem; they plugged in a fantasized increase in temp of 4.1 degrees Celsius. When you start with a fantasy, it’s no wonder that’s where you end up. If my granny had wheels she’d be a wagon. If I had a granny, that is.

If there is in fact more warmth, that means more vapor and clouds. More trees means more precipitation from capturing the vapor/clouds. It also means the snow and ice is more likely to melt intot heground and not sublimate. The assumptions of this study appears to be a zero sum game.But of course the clear intent is to raise yet more faux climate hysteria.

Peter, the American Southwest is in the DESERT! This is headshakingly stupid. Do you know where else is in the middle of a “mega-drought” – CHAD, EGYPT, LYBIA, ETHIOPIA, DJBOUTI, SAUDI ARABIA, ATACAIMA, NAZCA, and the rain-shadowed MOJAVE. These areas have been in multi-millenial droughts. It is because – wait for it – they are DESERTS! Just because California, Nevada, New Mexico, Arizona, Southern Utah, and Southern Colorado decided to urbanize in the middle of one does not make it any less of a desert. The San Fernado Valley is only useful because of three factors – irrigation, warm climate, and volcanic soils. BUT – it is still desert! Diverting irrigation to allow some silly chub or salamander to live is not a moral arguement that I wish to have.

If you are that worried about having enough fresh water to drink, move to Sierra Leone, Liberia, or Ghana: I hear they have plenty this time of year.

Now they are going to want to clear cut those areas to save the runoff rate? No! Here’s a perfect chance to move people out of the areas lacking water. Everybody to the cities! Let’s pack ’em in there.

Peter is all in. He’s worried. Every time he reads some climate article he get more convinced and alarmed.
He’s advocating the full Monty of climate action and is simply incapable of recognizing how mendacious the entire movement is.
We have 1000s and 1000s of Peters in Oregon.
Everyone of them thoroughly convinced earth and mankind are at grave risk.

The phenomenon is quite impressive in it’s cult like or parasitic nature.
There are simply too many millions of eco/green/sustainable/habitat invested activists who have hitched their causes to the AGW movement to make them ever let go.

California droughts come and they go. In the 1990s there was a 7 year drought. It ended and water increased. This current one will end too. Carlsbad is building after 12 years of Enviro Impact Studies, and various challenges in courts by enviros group, a major league desal facility. Will cost about a billion or so.Details can be found on the web. A dozen or so other similar projects litter the the cost North of there, but the Carlsbad is the first to actually break ground and employ people.

In the late 1800s some smart and industrious guys built a dam and a pipeline bringing Hetch Hechy water to SF Bay Area. Greening the Bay for generations to come. John Muir protested that action. Hence the heritage of the Sierra Club. Now 35 million claim California home, By Asian standards, this is rural. I expect this population to double in the next 50 years. Where will the water come from ?

I moved out and live in Nevada. I own a grape vineyard in the central valley. When we bought it the first thing I did was to expand the well water output. Our grapes are happy and will be harvested in about 4 weeks.

You make sense. Your comment reminds me of the Auburn dam, back in the day. It was close to completion, after the state spent more than a billion dollars on it [at a time when $1 billion was a lot of money].

Then the enviro crowd got involved, and managed to shut it down completely. Now the water runs straight to the ocean.

Is there anything that these eco groups do that is good for the state, or the country? The net result of their meddling always seems to leave people worse off than before. But the snail darters are happy, I guess.

I drive a couple of SUVs to compensate but they are still pretty effecfive (the enviros). Too bad about that Auburn dam. The California Water Resources system could use a few more dams. I’m not asking for 150 years of foresight like the Hetch Hetchy project, just another 50 years of scraping by so that the majority can shift towards a more conservative and pragmatic base (think more Chinese immigrants).

The authors found that greater vegetation density at higher elevations in the Kings basin with the 4.1 degrees Celsius warming projected by climate models for 2100 could boost basin evapotranspiration by as much as 28 percent, with a corresponding 26 percent decrease in river flow.

What models predict a 4.1C increase in temperature?

If there is an increase in the evapotranspiration of H2O, does that reduce the amount of temperature increase?

Will the increased rate of growth of plants reduce the increase of CO2 concentration?

Links
Abstract – 2002
Larry Bensona et al
Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada
……….Two high-resolution Holocene-climate records are now available from the Pyramid and Owens lake basins which suggest that the Holocene was characterized by five climatic intervals. TIC and δ18O records from Owens Lake indicate that the first interval in the early Holocene (11,600–10,000 cal yr BP) was characterized by a drying trend that was interrupted by a brief (200 yr) wet oscillation centered at 10,300 cal yr BP. This was followed by a second early-Holocene interval (10,000–8000 cal yr BP) during which relatively wet conditions prevailed. During the early part of the middle Holocene (8000–6500 cal yr BP), high-amplitude oscillations in TIC in Owens Lake and δ18O in Pyramid Lake indicate the presence of shallow lakes in both basins. During the latter part of the middle Holocene (6500–3800 cal yr BP), drought conditions dominated, Owens Lake desiccated, and Lake Tahoe ceased spilling to the Truckee River, causing Pyramid Lake to decline. At the beginning of the late Holocene (∼3000 cal yr BP), Lake Tahoe rose to its sill level and Pyramid Lake increased in volume.
=========================

Abstract – 1998
2000 Years of Drought Variability in the Central United States
…..Historical documents, tree rings, archaeological remains, lake sediment, and geomorphic data make it clear that the droughts of the twentieth century, including those of the 1930s and 1950s, were eclipsed several times by droughts earlier in the last 2000 years, and as recently as the late sixteenth century. In general, some droughts prior to 1600 appear to be characterized by longer duration (i.e., multidecadal) and greater spatial extent than those of the twentieth century…….
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Abstract – 2011
David W. Stahle et al
Tree-ring data document 16th century megadrought over North America
…….Droughts during the 1750s, 1820s, and 1850s–1860s estimated from tree rings were similar to the 1950s drought in terms of magnitude, persistence, and spatial coverage, but these earlier episodes do not appear to have surpassed the severity or extent of the Dust Bowl drought. However, longer tree-ring reconstructions of PDSI for the United States and precipitation for northwestern Mexico and western Canada indicate that the “megadrought” of the 16th century far exceeded any drought of the 20th century (Figure 1) [also see Wood-house and Overpeck, 1998], and is considered to be the most severe prolonged drought over much of North America for at least the last 500 years [Meko et al., 1995].
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Abstract – 2001
Steven L. Forman et. al.
Temporal and spatial patterns of Holocene dune activity on the Great Plains of North America: megadroughts and climate links
……High Plains showed peak activity sometime between ca. 7 and 5 cal. ka. Loess deposition between ca. 10 and 4 cal. ka also signifies widespread aridity…….. Periods of persistent drought are associated with a La Niña-dominated climate state, with cooling of sea surface temperatures in the tropical Pacific Ocean and later of the tropical Atlantic Ocean and the Gulf of Mexico that significantly weakens cyclogenesis over central North America. As drought proceeds, reduced soil moisture and vegetation cover would lessen evaporative cooling and increase surface temperatures. These surface changes strengthen the eastward expansion of a high-pressure ridge aloft and shift the jet stream northward, further enhancing continent-wide drought……..

I was watching ‘Location, Location, Location Australia’ last night. (my wife controls the remote.) They were looking at a shell of a house, all the internals removed because of the Brisbane floods. They pulled down a piece of mud left in the bones from the 1974 flood, that was about 3 foot higher than the latest one.